I think it just has to be your better judgement :) I have divided tanks, and 50/50 chance it doesn't work out. My halfmoon didn't mind a divided tank, my doubletail does not like it, my one female crowntail doesn't mind it, my baby betta doesn't mind it, my male VT doesn't like it... I've had to learn to pair up their personalities and "what they say goes"

Depends how heavily you plant the tank. Some fish will hide more than others, but generally there will be one or two always milling about, even if others are camped out somewhere.

I can tell you this about my sorority, the girls do whatever when I'm not watching. But when I come into view, and open the lid. They are out of the water as often as in it. While they can see you, and they know that hand means FOOOOOOD!!!!! You will get quite the show.

that said, there is no such thing as a totally non-aggressive betta, at least not one that's healthy. while some fish might be more aggressive (and who knows, it may divide down breed lines, but most evidence of that is anecdotal) but all bettas will be aggressive to one degree or another, and i don't really think it'd be responsible to put out guidelines for which fish would be safer in a divided setting than others based upon tail type. i've had some pretty laid-back plakats, and some EXTREMELY aggressive veiltails and halfmoons.

Evidence of highly aggressive strains in plakats are not anecdotal. You breed an aggressive female plakat to aggressive male and chances are high that you will reared aggressive plakats. Still, in general, plakats already have higher aggression than veiltails. In addition, I bred enough to know it's not anecdotal. Anyway, I said tail type is something to be aware of, but not entirely what should be considered. It's precautions I wanted to help point out to OP: Be careful, keep an watchful eye out if setup includes plakat females. I didn't tell OP that female plakats should be separated or that they are bound to kill each other.

Can we stay on the subject, and allow the OP to find the answers? Thanks All in all: 2 males no no, 2 females no - but a group of females yes. Some may not be able to be in a sorority? True. some males bettas cannot be in community tanks? true.